What’s that spot under my car??!!!

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What's that spot?

What Is That Fluid Leaking Under My Car?

Ever come out in the morning and say, “What the #$%$!!  is that spot under my car?????

Well that spot could or could not be serious but we have to figure it out.   In this blog we will cover the six most common fluid leaks from a car—from the leaks that will leave you stranded, to the leaks that should be in fact be happening. Yes, there are times when fluids should leak naturally from your car, and we will cover that as well. Let’s try to figure out what fluid is leaking from your car and what you should do about it.

Find the Source, Check the Color

First of all, before you start worrying, make sure the fluid leak is coming from your car and not the vehicle that was parked in that spot before you got there or from a previous time period. Just grab a flashlight, get down on one knee, and take a good look under your car.

If the fluid is coming from your car, you need to determine the fluid’s color. The best way to do that is to slide a piece of white cardboard or a piece of plywood under your car and let the car drip onto it. Capturing the drip this way will enlighten you in two ways: one, it will reveal the color, and two, it will give you a good indication of where the fluid is leaking from. First, without moving the board, notice where the drip is hitting the board; turn your head and look up from this point at the bottom of your car and see exactly where your leak is coming from. Once you have a clear view of where the fluid is leaking from, remove the board and check the color.

Different Fluids Have Different Colors

Six fluids dripped onto cardboard
Six fluids dripped onto cardboard

Six Most Common Fluids to Leak from a Car

The six fluids that most commonly drip from a car are:

  • water
  • motor oil
  • transmission fluid
  • coolant
  • gear oil, or differential fluid
  • and power steering fluid.

I left brake fluid out of this list, because it’s not common for brake fluid to leave a puddle under your car. Nevertheless a brake fluid leak is potentially serious (see my article about common brake problems). Just for quick reference, brake fluid color is clear to amber, and smells like fish oil; if you doubt me, take the cap off the brake fluid reservoir and sniff the cap.

1. Water Leaking From Your Car

The three H’s–hazy, hot and humid—are probably the most common cause of fluid leaking from a car, in the eastern U.S. at least. A car’s air conditioner needs to do something with the moisture it removes from the air inside the passenger compartment. It drains the water onto the ground under the car, via a rubber hose.

On very humid days, the water will pour out of the air conditioner drain onto the ground like from a faucet, until the cabin humidity is almost gone. This is what I meant earlier when I said that some leaks are supposed to happen.

This hose is usually at the front right (near the area where the passenger rests their feet) or in the middle of the cabin. If you have a newer minivan or large SUV with front and rear climate control, it’s possible to have two evaporators and two air conditioner drains, one in front and one in the rear.

Dual Climate Control

Dual climate control on a 2011 Honda Pilot. The rear controls are the blue and red arrows at right under “RR lock.” Fan speed is controlled from the rear controller.
Dual climate control on a 2011 Honda Pilot. The rear controls are the blue and red arrows at right under “RR lock.” Fan speed is controlled from the rear controller.

Here’s a tip: when you use the air conditioning system, it’s best to keep the recirculation button in the “on” position rather than the “fresh air” position (see picture below of the recirculation button on a Honda). If you leave the car in “fresh air” mode, it will continue to drag humid air into the car, the vehicle’s cabin will never reach optimum temperature, and sometimes when the weather is extremely humid, the air will turn into fog as it pours from your vents into your car’s passenger cabin. If you ever experience this phenomenon, reach over and push the recirculation button. The recirculated air will lose humidity on each pass through the evaporator, and your air conditioner will be working at maximum efficiency (see this article on how to defog car windows fast).

Recirculation Button

Recirculation button (at left) next to the fresh air button (at right) (2011 Honda Pilot). The recirculation button should be on when using air conditioning, but should not be on otherwise; it will fog up your windows.
Recirculation button (at left) next to the fresh air button (at right) (2011 Honda Pilot). The recirculation button should be on when using air conditioning, but should not be on otherwise; it will fog up your windows.

2. Oil Leaks

Engine oil, or “motor oil,” may vary in color from light amber to dark brown, depending on how well you maintain your car. If there is an oil leak, common sense tells you that it will be under the engine, but it’s not always immediately obvious where your engine is located. Don’t laugh: on a front-wheel-drive car, your engine could be located at the front left or front right, depending on where the transmission sits, and the engine could be in the rear of the car if you’re driving a Porsche or a VW bug. Once you figure out the oil is dripping from the engine, all you have to do is pinpoint the leak. You might want a mechanic to take a look at it if you can’t find exactly where it is leaking from. Oil leaks can come from some pretty obscure sources, like a crankshaft seal under the timing cover, or they can come from something easy to spot like a valve cover gasket.

If you know you have an engine oil leak, check your dipstick frequently. Do not drive a car that’s low on oil. It will overheat and damage itself. If you have a massive oil leak do not drive your car at all.

Oil Dipstick

Notice the brownish color of the motor oil or engine oil.
Notice the brownish color of the motor oil or engine oil.

3. Coolant or Antifreeze Leaks

Coolant comes in many colors now; it used to be green, but now its color depends on the manufacturer of the car or the coolant. Honda provides a blue coolant, Mercedes uses clear, Toyota uses red, and I have seen orange, green and all the colors of the rainbow. Coolant has a sweet smell, like candy, and also a sweet taste. Don’t taste it—it’s half ethylene glycol, which is poison—but I have tasted it a few times in my career, not by choice.

Coolant in the Overflow Tank

Honda brand coolant is blue.
Honda brand coolant is blue.

A coolant leak could be almost anywhere, because of all the coolant hoses that surround your engine. Some coolant hoses (the heater hoses) go into the passenger compartment itself. But the most common place for a coolant leak is your radiator, and that will be located behind the grill in the very front of the car.

If you suspect you have a coolant leak, you may be able to smell it. Take a quick glance at the coolant overflow tank, it is usually see-through and has “high” and “low” markings on it. If it’s empty, or you aren’t sure what you are seeing, let your engine cool completely and look in the radiator. (Do not remove the radiator cap on a hot engine. It could blow hot coolant or steam into your face and cause severe burns.) If you can’t see any coolant when you are peering down into the radiator, you may have a leak.

You don’t want to drive a car that has lost a massive amount of coolant. It can overheat and ruin the engine. Keep an eagle eye on the temperature gauge. Or better yet, tow it to where it can be fixed.

The Radiator Cap

Heed the warning! Don't take the cap off a hot radiator.
Heed the warning! Don’t take the cap off a hot radiator.
You should see coolant when you look inside the radiator.
You should see coolant when you look inside the radiator.

4. Transmission Fluid Leaks

Automatic transmissions use red or pink fluid, and lots of it. Very often, the first sign of an automatic transmission leaking is that the transmission will start to slip (the car will rev without going into gear). If the leak continues, eventually the car will not move at all.

Automatic transmissions use fluids specially formulated by the manufacturer. If you don’t use Honda-made automatic transmission fluid (ATF) in a Honda automatic transmission, you will compromise shift quality and void your warranty, so I recommend following Honda’s guidelines and using their recommended fluids.

Standard (“manual”) transmissions use gear oil (like heavy, strong-smelling motor oil; see “Gear Oil” below) or the manufacturer’s proprietary manual transmission fluid. Very old Hondas use regular motor oil in their standard transmissions.

The most common place for a transmission fluid leak on a front-wheel drive car is the axle seals; on a rear-wheel-drive car it is the output shaft seal. If you see red or pink fluid under your car, pull the transmission dipstick and check your transmission fluid level. Check the owner’s manual for the proper way to check transmission fluid, different manufacturers have different ways of checking transmission fluids. Some manufacturers don’t even let you check the fluid: the last model of the Honda Passport had no way of checking the transmission fluid—weird!

Honda Transmission Fluid

The end of the transmission fluid dip stick. Notice that the fluid is red.
The end of the transmission fluid dip stick. Notice that the fluid is red.

5. Gear Oil or Differential Fluid Leaks

Differential fluid, hypoid, gear oil, or gear fluid: whatever you call it, it’s very thick, it looks like honey, and it smells like a warm, greasy Mack truck sitting at a truck stop. If you get this stuff on your hands the smell doesn’t go away for days. Gear oil is dark brown, or dark amber if it’s new and clean. If your rear differential is leaking, or your standard transmission has a leak, you will find this fluid dripping. Gear oil can also leak from the wheel bearing seals or rear axle seals. Sometimes you will see oil being slung from the center of the wheel all over the wheel rim of the vehicle. Dust will collect on the wheel and turn black. If you have a four-wheel-drive car, gear oil can leak from the front axle as well. The smell alone will enable you to determine if it’s gear oil or not.

Share Your Experiences

If you have any questions about a fluid leak in your car, just leave me a comment in the comment section below and I will respond quickly. Your experiences are useful to me and others.

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